From 2001 to 2018 in Mari El Republic six-field fodder crop rotations including 1-3 fields of legume-cereal grasses were studied. The amount of plowed root-crop residues and nutrients entering the soil was assessed at different levels of minerals application (N60P60K60 and N90P90K90 in the 1st and 2 nd rotations, N60P60K60 и P60K60 in the 3rd rotation). During the research the total nitrogen content in sod-podzolic soil increased from 0.15% to 0.28%, the humus content raised from 1.82% to 2.53%. The largest amount of root-crop residues nutrients was plowed into 0 -20 cm soil layer during the fodder crop rotation at the 1-year use of the perennial grasses. On the average, it received 35.2 t/ha of dry matter, 560 kg/ha of nitrogen, 231 kg/ha of phosphorus and 338 kg/ha of potassium over 3 rotations. An increase in supply of soils with nitrogen and humus in the 3rd rotation raised the plant residues and nutrients accumulation to 49.9 t/ha, 821 kg/ha, 321 kg and 496 kg/ha, respectively. No significant differences were found between the fertilization backgrounds. In the structure of studied crop rotations cloveralfalfa-timothy grass mixture has made the greatest contribution to in the replenishment of nutrient elements by plowing up the root-crop residues: 10.1 tons of dry matter, 199 kg of nitrogen, 89 kg of phosphorus and 115 kg/ha of potassium. Using postcut mustard after winter rye provided almost the same amount of plowed root-crop residues as clover-alfalfa-timothy grass mixture.Conflict of interest: the authors stated that there was no conflict of interest.

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При наличии бобовых трав в структуре кормовых севооборотов возможно снижение эффективности внесения азотных удобрений на дерново-подзолистой почве. В этой связи проведена сравнительная оценка продуктивности шестипольных кормовых севооборотов с 16%, 33 и 50% насыщенностью бобово-злаковыми травосмесями на фоне внесения минеральных удобрений (Р60К60, N60Р60К60). Исследования проводили в 2013-2017 гг. в условиях Республики Марий Эл. Установлено, что продление срока использования многолетних бобово-злаковых трав в изучаемых кормовых севооборотах на один год сопровождалось увеличением сбора сухого вещества на 1,1-2,1 т/га, обменной энергии-на 6,7-16,5 ГДж/га, сырого протеина-на 2,3-3,7 ц/га. Длительное внесение минерального азота сопровождалось тенденцией роста продуктивности кормовых севооборотов с многолетними бобово-злаковыми травами на 9-21%. При этом однолетние и озимые культуры, изучаемые в севооборотах, за исключением однолетних трав с подсевом многолетних трав в условиях 2013 г., обеспечивали достоверные прибавки продуктивности. Наибольший прирост продуктивности отмечается в первом севообороте, где многолетний агроценоз используется всего 1 год. Внесение минерального азота в большей мере сопровождалось повышением сбора сырого протеина, чем других показателей продуктивности изучаемых культур кормовых севооборотов.

It is known that significant saving of nitrogen fertilizers are due to perennial legume-cereal grasses use in crop rotations. From 2013 to 2018in the Mari El Republic six-field grass-grain fodder crop rotations were compared on sod-podzolic soils with a very high level of phosphorus and potassium. In the third rotation their productivity and bioenergetic efficiency, changes in several important soil fertility indicators, and crud protein content in the produced fodder were evaluated. The main difference between the crop rotations was based on the duration of the clover-alfalfa-timothy grass mixture (CAG) use: from one year to three years. In given experiment there was also studied the effect of mineral nitrogen (variants N0, N60) against Р60К60 background on the yield of crop rotations. During six years, there was no significant soil acidification in the variants. Each additional year of clover-alfalfa-timothy grass mixture use raised the energy efficiency ratio of crop rotations by 24-47 % (from 1.13-1.24 by one-year use to 2.08-2.25 by three years of use). Three-year CAG use as compared with one- and two-years has given to the crop rotation significant advantages in energy efficiency (up to two times) and productivity (approximately 40-80 %) of cultivated crops. After refusing to apply nitrogen fertilizations in such crop rotation, average crop productivity, soil humus and nitrogen content in the soil were better preserved. The average crude protein content in dry matter of the obtained fodder increased from 12.7 % to 14.6 % when prolonging theca use up to two years. The average energy value of the yield per rotation was recorded low (8.4-8.7 MJ/kg) and did not depend on the studied factors.